Most roadways throughout the world are paved with asphalt concrete mixes. Typically, the hot asphalt road mix containing asphalt cement, aggregate, and antistripping agents is produced at an asphalt plant and transported to the construction site in the beds of dump trucks. One of the problems encountered in delivering road asphalt in dump trucks is that the asphalt tends to stick to the metal surfaces of the truck beds. Making this problem worse is the recent trend toward the use of polymer-modified road asphalt mixes which form more tenacious bonds with the truck bed surfaces.
The sticking prevents the asphalt from smoothly sliding out as the dump truck discharges its load. Workers are thus required to expend considerable time and energy to manually scrape the asphalt out of the truck bed with shovels. Most often, however, solidified pieces of asphalt remain adhered to the bed despite the workers best efforts. Asphalt is wasted and material usage suffers. Furthermore, as the hardened deposits build up in the truck bed, the quality of subsequent road mixes is also affected. The adherent pieces eventually fall off as large solid inclusions in subsequent road mixes. Often, the inclusions cause the road paving equipment to tear up the road membrane as the asphalt is laid down.
One approach taken to solve this problem has been to spray asphalt release agents over the truck bed surfaces to prevent asphalt adherence. A popular asphalt release agent used in the past was hydrocarbon fuel such as ordinary diesel fuel. Diesel fuel was extremely effective in cutting and dissolving the asphalt in order to prevent it from sticking. However, diesel fuel has since been outlawed as an asphalt release agent. It presented too many soil and ground water contamination risks and also when not used properly decomposed the asphalt. Other fuel-based release agents such as hydrocarbon wax emulsions have been banned as well, since they also damaged the structural integrity of the contacted asphalt, resulting in inferior and shorter-lasting roads. Furthermore, all release agents which rely upon decomposition or degradation of the contacted asphalt are no longer considered desirable.
Non-fuel based asphalt release agents which provide slippery surfaces on the truck bed to prevent the asphalt from sticking without decomposing the asphalt have also been tried. For instance, U.S. Pat. No. 5,332,554 (DeLong) discloses a foam asphalt release agent including an aqueous solution of an inorganic salt, such as magnesium chloride or calcium chloride, together with a foaming agent, such as an anionic isopropyl alcohol surfactant, a metal corrosion inhibitor, such as sodium phosphate ester, and optional dye. U.S. Pat. No. 5,494,502 (DeLong) discloses another non-fuel based foam asphalt release agent including an aqueous mixture of a fatty oil, together with a foaming agent, such as an anionic surfactant, optional emulsion stabilizer, such as crosslinked polymer microgels, optional alkalinizing agent, such as triethanolamine, and optional preservative or antimicrobial agent, such as sodium benzoate. U.S. Pat. No. 5,407,490 (Zofchak) discloses still another asphalt release agent comprising a water-based mixture of monomethyl coconate esters together with ethoxylated sorbitan ester emulsifiers. These non-fuel based release agents, however, suffer from not being especially effective in releasing the more tenaciously adhered pieces of polymer-modified asphalt from the truck beds, which traditionally have been more difficult to handle. Other non-fuel based release agents have also been tried, but most of these suffer from being limited in ineffectiveness, environmentally hazardous, thermally unstable, costly, or complex in preparation, delivery, or application.
It would be desirable to provide a more effective asphalt release agent which does not suffer from the foregoing disadvantages. Yet, from a practical standpoint, this is difficult because of the stringent requirements that must be satisfied. For instance, economics are extremely important in the asphalt industry due to the large scale of potential application. Thus, any material proposed for use as an asphalt release agent must be very inexpensive, which eliminates many potential candidates. Another important criteria is that the release agent must be derived from relatively high boiling, thermally stable materials that will not substantially decompose and volatilize when contacted with the hot asphalt road mix, which is usually loaded at the asphalt plant onto the truck beds at temperatures typically above 325.degree. F. The release agent should also have a sufficiently high flash point to avoid flammability hazards which may be encountered at the asphalt plant or construction site. Moreover, the release agent should be environmentally friendly, physiologically safe, relatively non-corrosive to human skin, easy to prepare, deliver and apply even in extreme cold weather conditions, and should not degrade the contacted asphalt in any manner that would impair the road quality. And all of the above requirements must be satisfied, while also providing a material possessing effective asphalt release action, especially with respect to polymer-modified asphalt.
What is needed is an asphalt release agent that is exceptionally effective in preventing the sticking of asphalt, especially asphalt containing polymers, to truck beds and other surfaces, is environmentally friendly and physiologically safe, is inexpensive, is easy to prepare, deliver and apply even in extreme cold temperatures, is thermally stable and long-lasting, is non-flammable, and does not compromise the quality of asphalt laid down in the road.